Resonator tuner



Jan. 17, 1956 M. R. HUBBARD 2,731,604

RESONATOR TUNER Filed Sept. 18, 1952 IN V EN TOR. A/f/Plf 19005460 United States Patent RESONATOR TUNER Merle R. Hubbard, Cedar Rapids, Iowa, assignor to C01- lins Radio Company, Cedar Rapids, Iowa, a corporation of iowa Application September 18, 1952, Serial No. 310,289

3 Claims. (Cl. 333-82) This invention relates in general to high frequency tuners and in particular to cavity resonator tuners.

Cavity or coaxial resonators are used extensively .at ultra high and very high frequencies as tuned circuits. It has been customary to construct cavity resonators with inner and outer conductors. They are shorted at one end and the lengths of the inner and outer conductors are such that the entire assembly will tune to a desired frequency with a certain value of loading capacity at the open end. Various methods have been used to make such elements continually tunable over a frequency range. One method is to use a shorting plunger between the inner and outer conductor that lengthens or shortens the efiective length of the cavity. Another method is by using a variable condenser across the open end of the coaxial resonator.

An object of the present invention is to provide an improvement in tunable cavity resonators wherein a very accurate response may be obtained.

Further objects, features and advantages of the invention will become apparent from the following description and claims when read in view of the drawings, in which:

Figure 1 illustrates one modification of a coaxial tunable resonator according to my invention,

Figure 2 is a modification of my invention, and

Figure 3 illustrates a third modification.

Figure 1 illustrates a cylindrical member which has a conducting disc 11 across one of the open ends. A shorting disc 12 is mounted to a plurality of downwardly extending wires 13. One of the wires 14 is connected to the plate 11 and the remaining ones pass through openings 15 formed in the plate 11 so that they are insulated from it.

An end loading capacitor C1 is connected between the upper end of the cylinder 10 and the disc 12. The cylinder 10 is grounded.

A lead 16 extends from the cylinder 19 to a multiple switch, designated generally as 17. The switch 17 has a plurality of movable members 18 that may be pivoted downwardly to engage the ends 19 of the rods 13. The members 18 are connected together electrically.

Various combinations of the switches 18 engaging the lower ends 19 of the wires 13 cause the resonant frequency of the cavity resonator to change. As more wires are shorted together by the switches 18, the characteristic impedance of the cavity is progressively reduced resulting in a higher resonant frequency. With the structure shown in Figure 1, the increments of frequency become smaller and smaller as more wires are shorted. The following ice '2 table illustrates the results obtained with different values of C11 Load capacities used and resultant resonant frequencies Number of wires shorted to base 3 mil. 9 Auf. 19 pi.

7 Me. Me. Me. 1 232 195 210 245 275 300 320 332 345 The apparent action of the structure shown in Figure 1 is that when only one wire 14 acts as the inner conductor, the characteristic impedance of the cavity is high but as each successive wire is shorted the characteristic impedance is decreased and the resonant frequency goes up. One wire is used as an inner conductor and the other wires appear as capacity across the circuit. This capacity is reduced as the wires are shorted together and at the same time the characteristic impedance is lowered.

A modification of the invention is shown in Figure 2 wherein a U-shaped conductor comprises a first leg 20 that has its lower end shorted to a disc 11. A transverse portion 21 is adjacent the opposite end of the member 20, and a downwardly extending portion 22 terminates above the disc 11.

A second conductor 23 extends downwardly from the member 21 and terminates above the disc 11. A shorting plunger 24 engages the members 20, 22 and 23. As the shorting plunger 24 moves from member 11 toward member 21, the conductors 2t 22 and 23 are first in parallel, but when the shorting plunger reaches the member 21 the conductors 22 and 23 form capacity applied across the condenser C1 and the only inductance in the circuit at this point is the conductor 20.

The plunger 24 extends through an opening 25 formed in the disc 11 and may be manually or automatically moved longiutdinally of the cylinder 10. As the shorting bar travels from adjacent the disc 11 toward the member 21, the frequency will be tuned from a high to a low frequency. The etfect is to change the characteristic impedance from low to a higher impedance.

A third modification is illustrated in Figure 3 wherein the cylinder has been replaced by a rectangular shield member 26. A strip of conducting material 27 has one end 28 connected to an end 29 of the cover member and extends upwardly and downwardly to form a leg 30 which terminates above the end 29.

The end loading capacitor C1 is connected from the end 39 to the cover member. A shorting plunger 32 shorts from the leg 27 to the leg 30 and may be moved longitudinally thereof.

A sheet of mice may be placed between the leg 30 and the wall 33 of the cover member to decrease the characteristic impedance when the shorting bar is adjacent the end 29. When the shorting plunger 32 is adjacent the end 29, the characteristic impedance of the cavity is low and the frequency high. When the shorting plunger is near condenser C1, member 30 and mica or other dielectric between the member 30 and the wall 33 appear to be capacitive'across C1. The inductance of the center conductor is only the member 27 which is so spaced from the sides of the container so as to give a higher impedance. With such a structure, applicant has been able to tune from 280 to 360 megacycles.

It is seen that the invention described herein relates to an ultra high and very high frequency tuner wherein a continuous tuning characteristic may be obtained.

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited as changes and modifications may be made therein which are Within the full intended scope of the invention as defined by the appended claims.

I claim:

l. A resonator tuner comprising, a hollow, conductive cylindrical member, a conducting disc attached to one end of said cylindrical member, a first wire having one end attached to said disc and extending into the confines of said cylinder, a shorting disc insulated from said cylinder and attached to the opposite end of said first wire, a plurality of other wires attached to said shorting disc and extending through said conducting disc, a plurality of openings formed in said conducting disc to allow said plurality of wires to extend therethrough, and a multiple switch connected to said conducting disc and including means to conductively connect the free ends of said plurality of wires. a

2. A resonator tuner comprising, a hollow, conductive cylindrical member, a conducting disc attached to one end of said cylindrical member and formed with a plurality of openings, :1 shorting disc within said cylindrical memone of said wires attached to said conducting disc and the remainder of said wires extending through openings formed in said conducting disc, and a multiple switch with one side connected to said cylindrical member and formed with a plurality of contacts to conductively connect the free ends of said wires that pass through said conducting disc.

3. A tunable cavity resonator comprising, a hollow, conductive cylindrical member, a conducting disc attached across one end of said cylindrical member and formed with a plurality of openings, a shorting disc mounted within and insulated from said cylindrical member, a plurality of wires having one end attached to said shorting disc about its periphery, a first of said wires with its opposite end connected to said conducting disc, the remainder of said wires extending through the openings formed in said conducting disc and insulated therefrom, a multiple switch with a common side connected to said cylindrical member and a plurality of contacts to conductively connect, respectively, with the free ends of said wires, and a condenser connected between said shorting disc and said cylindrical member.

References Citedin the file of this patent UNITED STATES PATENTS 7 

